It is well known in the prior art to provide autonomous carriers or vehicles with a systems for guidance and navigation, together with a sensing system for obstacle detection. The sensing system generally sweeps around the horizon in a manner similar, for example, to a ship's radar. Systems of these types are often used with surface treatment apparatuses such as autonomous or robotic vacuum cleaners as, for example, are disclosed in International Patent Applications WO 97/41451 (U.S. Pat. No. 5,935,179) and WO 00/38028. The autonomous surface treatment apparatuses generally have a main body supported on or by a number of motor-driven wheels or rollers and include means for surface treatment, such as a rotating brush in combination with a vacuum cleaning device.
The foregoing devices normally employ a microprocessor, together with appropriate software, for controlling the operation of the devices. Typically, the microprocessor receives input data from the wheels and sensing system for the purpose of enabling the position of the device to be fixed, as well as the locations of any walls and obstacles to be determined. This input data is then used as the basis for navigating the autonomous apparatus so that, for instance, it will be able to perform a cleaning function or other surface-treatment function according to a predetermined strategy while at the same time avoiding collisions with any obstacles and barriers such as walls, tables, bookcases or the like.
Many robotic vacuum cleaners in use today initiate their cleaning task by tracking the walls of the room to be vacuumed. Thereafter, they continue their function by moving in a random pattern over the room until the control systems for the cleaners estimate that the entire room, apart from where obstacles are located, has been cleaned. Although this strategy can work quite well, more often than not it results in the vacuum cleaner going over the same area several times, while other areas remain uncleaned even after an extended period of operation.
The issue of providing a more efficient strategy for navigating an autonomous surface treatment apparatus over a given area has been addressed in the prior art. For example, U.S. Pat. No. 4,674,048 relates to a guidance system for a mobile robot, which system is based on the creation of a grid-like map for the surface to be treated. Columns and rows are defined on the grid. The system studies and stores a travelling range to be used and guides the robot through a travel pattern within the specified range by sequentially moving the robot back and forth along one of the columns and rows of the map and shifting the robot to other columns and rows. In response to the detection of an obstruction, the robot shifts to the next column and row by turning the robot at the point where the obstruction is sensed. In this way, the robot travels within the defined range, without leaving any area untravelled, while obstructions are recognized and the robot's course is altered in response to those obstructions.
U.S. Pat. No. 5,440,216 relates to a mobile robot cleaner which initially follows the walls of a room to be cleaned to note their location and, thereby, establish the configuration and size of the room. The cleaner's control system then compares this information with data previously stored to select a control program for a room that is the most like to the room to be cleaned. The cleaner then performs the cleaning operation according to the selected program, moving in parallel lines within the configuration of the room that the robot has established.
International Patent Application WO 99/59402 discloses a robot that has a sensor unit and a navigation system. The sensor unit senses the proximity of the robot to markers located along the outer boundary of an area or field of operation to be covered. The navigation system guides the robot, generally, in straight, parallel lines and causes the robot to turn when it encounters a boundary marker.
International Patent Application WO 00/38025 discloses an autonomous floor-cleaning device arranged so that it first traverses the boundaries of a room and, thereafter, moves inward and completes a second circuit of the room. The device continues to move further inward after each circuit it makes until the room, apart from areas occupied by obstacles, has been cleaned, the entire cleaning path, generally, defining an inwardly, spiraling pattern of movement.
Although the above strategies can be used with satisfactory results, the efficiency with which they are implemented is less than desired in most practical cases, particularly where there are obstacles of various sizes and forms present that constantly interrupt the nominal path of the autonomous apparatus. In particular, the strategy of moving the autonomous apparatus back and forth, generally, in straight, parallel lines will be disrupted in environments where elongated obstacles are present, especially when some of the elongated obstacles are arranged perpendicularly to the movement of the apparatus.
Consequently, there remains a need for an efficient and effective strategy for navigating an autonomous surface-treatment apparatus over a given field of operation.